A data processing device, typically represented by Computer Numerical Control apparatus (CNC) and robot controllers, comprises one or more processors, a chip set that realizes a predetermined function in collaboration with the processors, a bus that communicates data between the processors and the chip set, and a boot Read Only Memory (ROM) that stores a boot program for initializing the data processing device after powering thereon, and the like. Conventionally, a parallel bus is used as a bus for such a data processing device (for example, Patent Literature 1 and Patent Literature 2).                Patent Literature 1: JP-A-2002-140205        Patent Literature 2: JP-A-2003-114800        
In recent years, a serial bus, such as Peripheral Component Interconnect (PCI) Express, tends to be used as a bus of a data processing device, instead of a parallel bus, in order to communicate data between the processor and the chip set with a higher speed. There are serial buses, such as a PCI Express that use the processor as a root complex, that is not allowed to be initialized from the chip set side before use. Such serial buses are required to be initialized by the processor based on a boot program before use. In such a case, the processor is difficult to acquire a boot program through the serial bus. Therefore, in order for the processor to initialize the data processing device after powering, the processor needs to be connected to an external boot ROM using a boot bus that does not require initialization based on a boot program before use.
When a data processing device uses a serial bus that requires initialization based on a boot program before use, in order to initialize the serial bus, the number of boot ROMs needs to be increased in accordance with the increase in the number of the processors equipped on the data processing device. This results in the mounting area of the boot ROMs having to be expanded and costs are increased.
The objective of the present invention is to provide a data processing device that can initialize a serial bus without increasing the number of boot ROMs in accordance with the increase in the number of the processors, even when the serial bus requires initialization based on a boot program before use.